I have an Apple II+, and a compact floppy disk drive with an Apple II disk interface card.
First, a description of a previous problem:
I have had problems with the Apple not booting if the disk interface card is plugged in. It seemed like the card's PROM is sucking power through the data bus due to internal clamping diodes. The PROM's +5V supply is disconnected when the /I/O SELECT signal is inactive (high), so I tried bypassing the circuit so that the PROM is always powered (this is not a good idea when using many peripheral cards but I had only the disk interface card). This worked much better, as the drive now lights up and spins when powering the Apple. I should perhaps mention that I've replaced a failing 8T28 transceiver with a 74HC245, which I guess could be part of the problem.
This is the current problem:
Now I cannot properly boot the Apple with a DOS 3.3 disk I have. It seems like the Apple reads for a few seconds, then exits with something like this:
*9D10 A=34 X=10 Y=35 S=9A
That's NOT the exact output, just a general idea of how it looks. I don't have access to the Apple right now (at work!). I think the disk is OK, but I'm gonna test it when I get my hands on the Apple IIe I have elsewhere...
So my questions are:
1) why is the Apple not working properly when disk interface card is plugged in?
2) what is the meaning of the output I get when trying to boot DOS, and how do I fix it?
3) what should the Apple do when there is no disk in the disk drive? does it spin endlessly?